Older versions of Catalina can fail to erase the System and Data volumes, but 10.15.6 should be able to, making clean re-installation simpler.
Follow Apple’s instructions for a clean re-install, and you’ll probably hit an error, and be left floundering in Recovery mode with an unbootable system.
When you go to perform a clean re-install of Catalina, what should you do? Which volume(s) to erase or delete, and how to fix problems?
Should you install, re-install, or clean (re-)install macOS? Why, how to, and what they entail.